Various cardiovascular, neurosurgical, pulmonary and other interventional procedures, including repair or replacement of aortic, mitral and other heart valves, repair of septal defects, congenital defect repairs, pulmonary thrombectomy, coronary artery bypass grafting, angioplasty, atherectomy, treatment of aneurysms, electrophysiological mapping and ablation, and neurovascular procedures, may require general anesthesia, cardiopulmonary bypass, and arrest of cardiac function. In such procedures, the heart and coronary blood vessels are isolated from the remainder of the circulatory system. This serves several purposes. First, such isolation facilitates infusion of cardioplegic fluid into the coronary arteries to perfuse the myocardium and arrest cardiac function without allowing the cardioplegic fluid to be distributed elsewhere in the patient's circulatory system. Second, such isolation facilitates use of a cardiopulmonary bypass system to maintain circulation of oxygenated blood throughout the circulatory system without allowing such blood to reach the coronary arteries and resuscitate the heart. Third, in cardiac procedures, such isolation creates a working space into which the flow of blood and other fluids can be controlled or prevented so as to create an optimum surgical environment.
One medical procedure of particular interest to the present invention is the treatment of heart valve disease. Co-owned, copending patent application Ser. No. 08/281,962 and Ser. No. 08/486,216, which are incorporated herein by reference, describe methods of performing closed-chest or thoracoscopic heart valve replacement surgery. Isolating the heart from the systemic blood circulation, inducing cardioplegic arrest and establishing cardiopulmonary bypass are important steps in the performance of the heart valve replacement procedure.
The endovascular system includes an elongated aortic partitioning catheter having an occluding member on a distal portion of the catheter adapted to occlude a patient's ascending aorta. The catheter preferably has an inner lumen extending within the catheter to a port in the distal end of the catheter. The catheter is adapted to be inserted into the patient's arterial system (e.g. through the femoral or brachial arteries) and advanced to the ascending aorta where the occluding member is expanded to occlude the aorta. The occluding member separates the left ventricle of the heart and an upstream portion of the ascending aorta from the rest of the patient's arterial system. Thus, the catheter provides an endovascularly inserted, internal vascular clamp, similar in function to the external "cross-clamp" used in open cardiac surgical procedures. The internal clamp is less traumatic to the clamped vessel and provides a lumen or working channel through which instruments or fluids may be passed into or withdrawn from the area upstream of the distal end of the clamp.
Also included with the system is a cardiopulmonary bypass system which withdraws blood from the patient's venous system, e.g. the femoral or jugular vein, removes CO.sub.2 and adds oxygen to the withdrawn blood, and returns the oxygenated blood to the patient's arterial system, e.g. the femoral or brachial artery. The system is also provided with a device for infusing fluid containing cardioplegic material (e.g. an aqueous solution of KCl and/or magnesium procaine and the like) through the coronary arteries so as to temporarily paralyze the myocardium.
A preferred method for inducing cardioplegic arrest of a heart in situ in a patient's body, includes the steps of:
(a) maintaining systemic circulation with peripheral cardiopulmonary bypass; PA0 (b) partitioning the coronary arteries from the ascending aorta by, e.g., occluding the ascending aorta through a percutaneously placed arterial balloon catheter; PA0 (c) introducing a cardioplegic agent into the coronary circulation; and PA0 (d) venting the heart.
The method may be carried out on humans or other mammalian animals. The method is of particular applicability in humans as it allows an alternative approach to open heart surgery and the development of closed cardioscopic surgery. The method enables a percutaneous bypass system to be associated with cardioplegia, venting and cooling of the heart which overcomes the need for a median sternotomy.
In a preferred embodiment, the occluding member is an inflatable cuff or balloon of sufficient size to occlude the ascending aorta. The length of the balloon should preferably not be so long as to impede the flow of blood or other solution to the coronary arteries or to the brachiocephalic, left carotid or left subclavian arteries. A balloon length of about 20-40 mm and diameter of about 35 mm is suitable in humans. The balloon may be cylindrical, spherical, ellipsoidal or any other appropriate shape to fully and evenly accommodate the lumen of the ascending aorta. This maximizes the surface area contact with the aorta, and allows for even distribution of occlusive pressure.
The balloon is preferably inflated with a saline solution mixed with a radiopaque contrast agent to avoid introducing an air embolism if the balloon ruptures. The balloon should be inflated to a pressure sufficient to prevent regurgitation of blood into the aortic root and to prevent migration of the balloon into the root whilst not being so high as to damage the aorta. An intermediate pressure of about 350 mm Hg, for example, is preferred.
The aortic partitioning catheter is preferably introduced under fluoroscopic guidance over a guidewire. Transoesophageal echocardiography can also be used for positioning the aortic catheter. The catheter may serve a number of separate functions and the number of lumina in the catheter will depend upon how many of those functions the catheter is to serve. The catheter can be used to introduce the cardioplegic agent, normally in solution, into the aortic root via one lumen. The luminal diameter will preferably be such that a flow of the order of 100-500 ml/min of cardioplegic solution, and more preferably 250-500 ml/min, can be introduced into the aortic root under positive pressure to perfuse the heart by way of the coronary arteries. The same lumen can, by applying negative pressure to the lumen from an outside source, effectively vent the left heart of blood or other solutions. The cardioplegic agent may be any known cardioplegic agent. The agent is preferably infused as a solution into the aortic root through one of the lumina of the aortic catheter.
It may also be desirable to introduce medical instruments and/or a cardioscope into the heart through another lumen in the catheter. The lumen should be of a diameter suitable to pass a fiberoptic light camera of no greater than 3 mm diameter. It is, however, preferable that the diameter and cross-section of the internal lumina are such that the external diameter of the catheter is small enough for introduction into the adult femoral artery by either percutaneous puncture or direct cutdown.
The oxygenated blood returning to the body from the bypass system is conveyed into the aorta from another lumen in the cannula carrying the balloon. In this case, the returning blood is preferably discarded from the catheter in the external iliac artery. In another embodiment of the invention, and in order to reduce the diameter of the catheter carrying the balloon, a separate arterial catheter of known type may be used to return blood to the patient from the bypass system. In this case a short catheter is positioned in the other femoral artery to provide systemic arterial blood from the bypass system. The control end of the catheter, i.e. the end that remains outside the body, should have separate ports of attachment for the lumina. The catheter length should be approximately 900 mm for use in humans.
With the heart paralyzed, the expandable member is expanded within the ascending aorta, and with the cardiopulmonary bypass operating, the heart is prepared for a cardiac procedure. While a particularly attractive feature of the invention is that it prepares the heart for endovascular, thoracoscopic, and other minimally-invasive procedures, the invention can also be used to prepare the heart for conventional open-heart surgery via a thoracotomy. It should also be noted that, if during an endovascular cardiac procedure in accordance with the invention, it becomes necessary to perform an open-heart procedure, the patient is already fully prepared for the open-heart procedure. All that is necessary is to perform a median sternotomy to expose the patient's heart for the conventional surgical procedure.
The endovascular device for partitioning the ascending aorta between the coronary ostia and the brachiocephalic artery preferably includes a flexible shaft having a distal end, a proximal end, and a first lumen therebetween with an opening at the distal end in communication with the first lumen. The shaft has a distal portion which is shaped for positioning in the aortic arch so that the distal end is disposed in the ascending aorta pointing toward the aortic valve. The first lumen may be used to withdraw blood or other fluids from the ascending aorta, to introduce cardioplegic fluid into the coronary arteries for paralyzing the myocardium, and/or to introduce surgical instruments into the ascending aorta, the coronary arteries, or the heart for performing cardiac procedures.
In one embodiment, the distal portion is shaped so that the distal end of the shaft is spaced apart from any interior wall of the aorta and the distal end is aligned with the center of the aortic valve. By "shaped," it is meant that the distal portion of the shaft is preset in a permanent, usually curved or bent shape in an unstressed condition to facilitate positioning the distal portion within at least a portion of the aortic arch. A shaft is preferably for straightening the preshaped distal portion. Usually, the straightening means comprises a straightening element slidably disposed in the first inner lumen having a stiffness greater than the stiffness of the preshaped distal portion. The straightening element may comprise a relatively stiff portion of a flexible guidewire extending through the first inner lumen, or a stylet having an axial passage through it for receiving a movable guidewire. Although it is preferred to provide a shaped-end and a straightener, the shaped-end may be imparted to the distal portion of the shaft with a shaping or deflecting element positioned over or within the shaft.
The balloon may be made of an elastomeric material, such as polyurethane, silicone or latex. In other embodiments, the occlusion means may be an inflatable balloon made of a nondistensible balloon material, such as polyethylene, polyethylene terephthalate polyester, polyester copolymers, polyamide or polyamide copolymers. The balloon is further configured to maximize contact with the aortic wall to resist displacement and prevent leakage around the balloon, preferably having a working surface for contacting the aortic wall with a length in the range of about 1 to about 7 cm, more preferably in the range of about 2 to 5 cm, when the balloon is expanded to fully occlude the vessel.
When a balloon is used for the occluding means, the endovascular device has an inflation lumen extending through the shaft from the proximal end to the interior of the balloon, and means connected to the proximal end of the inflation lumen for delivering an inflation fluid to the interior of the balloon.
The shaft of the endovascular device may have a variety of configurations. The first inner lumen and inflation lumen may be coaxial, or a multilumen design may be employed. The shaft may further include a third lumen extending from the proximal end to the distal end of the shaft, allowing pressure distal to the occluding means to be measured through the third lumen. The shaft may also include means for maintaining the transverse dimensions of the first inner lumen, which may comprise a wire coil or braid embedded in at least the distal portion of the shaft to develop radial rigidity without loss of longitudinal flexibility. The shaft preferably has a soft tip at its distal end to prevent damage to the heart valve if the catheter comes into contact with the delicate valve leaflets.
The shaft preferably has a length of at least about 80 cm, usually about 90-125 cm, to allow transluminal positioning of the shaft from the femoral and iliac arteries to the ascending aorta. Alternatively, the shaft may have a shorter length, e.g. 20-60 cm, for introduction through the iliac artery, through the brachial artery, through the carotid artery, or through a penetration in the aorta itself.
The shaped distal portion of the device maintains the distal end in a position spaced apart from the interior wall of the ascending aorta so that the distal opening is unobstructed and generally aligned with the center of the aortic valve. This facilitates aspiration of blood, other fluids, or debris, infusion of fluids, or introduction of instruments through the distal opening in the endovascular device without interference with the aortic wall or aortic valve tissue. The method may further include, before the step of introducing the shaft into the blood vessel, the steps of determining a size of the patient's aortic arch, and selecting a shaft having a shaped distal portion corresponding to the dimensions and geometry of the aortic arch.
Thus, using the aforementioned system and method, a patient's heart can be arrested and the patient placed on cardiopulmonary bypass without a thoracotomy, thereby reducing mortality and morbidity, decreasing patient suffering, reducing hospitalization and recovery time, and lowering medical costs relative to open-chest procedures. The endovascular partitioning permits blood flow through the ascending aorta to be completely blocked between the coronary ostia and the brachiocephalic artery in order to isolate the heart and coronary arteries from the remainder of the arterial system. This has significant advantages over the aortic cross-clamps used in current cardiac procedures, not only obviating the need for a thoracotomy, but providing the ability to stop blood flow through the aorta even when calcification or other complications would make the use of an external cross-clamp undesirable.
The system and method may further be useful to provide cardiopulmonary bypass during endovascular interventional procedures in which cardiac function may or may not be arrested. Such procedures may include angioplasty, atherectomy, heart valve repair and replacement, septal defect repair, treatment of aneurysms, myocardial mapping and ablation, myocardial drilling, and a variety of other procedures wherein endovascular interventional devices are introduced through the bypass cannula of the invention and advanced into the heart or great vessels. In this way, the invention facilitates cardiopulmonary bypass during such procedures without requiring additional arterial or venous penetrations.
The aforementioned applications and patents describe an endovascularly positionable occluding member which is used to occlude the ascending aorta of the patient. Because of its proximity to the left ventricle, the occluding member is subject to pressure forces on both sides of the balloon. Pressure forces are developed, for example, from the outflow of blood during systole. Such forces threaten to displace the occluding means either downstream, where it might occlude the ostium of the brachiocephalic or other artery, or upstream where the occluding member might damage the aortic valve or occlude the coronary ostia. Advantageously, the shape of the distal end of the endovascular device described above is configured to help maintain the position of the occluding member in the ascending aorta against the force of systolic outflow as the occluding member is expanded and retracted, as well as during the period in which the occluding member fully occludes the aorta but the heart remains beating.
Although the shaped distal end of the above-described endovascular occluding member helps to prevent migration of the occluding member, further features which reduce migration are desirable given the potentially catastrophic consequences of occluding member migration.